<!-- 业务技术点总结：
1.渲染功能（不及格高亮）
v-if v-else v-for v-bind:class
2.删除功能
点击传参 filter过滤覆盖原数组
.prevent阻止默认行为
3.添加功能
v-model v-model修饰符(.trim.number)
unshift修改数组更新视图
4.统计总分，求平均分
计算属性reduce求和 -->
<link rel="stylesheet" href="./styles/index.css" />
<div id="app" class="score-case">
  <div class="table">
    <table>
      <thead>
        <tr>
          <th>编号</th>
          <th>科目</th>
          <th>成绩</th>
          <th>操作</th>
        </tr>
      </thead>
      <tbody v-if="list.length>0">
        <tr v-for="(item,index) in list" :key="item.id">
          <td>{{index+1}}</td>
          <td>{{item.subject}}</td>
          <td :class="{red:item.score < 60}">{{item.score}}</td>
          <td><a href="#" @click.prevent="del(item.id)">删除</a></td>
        </tr>
      </tbody>
      <tbody v-else>
        <tr>
          <td colspan="5">
            <span class="none">暂无数据</span>
          </td>
        </tr>
      </tbody>

      <tfoot>
        <tr>
          <td colspan="5">
            <span>总分：{{Total}}</span>
            <span style="margin-left: 50px">平均分：{{average}}</span>
          </td>
        </tr>
      </tfoot>
    </table>
  </div>
  <div class="form">
    <div class="form-item">
      <div class="label">科目：</div>
      <div class="input">
        <input type="text" placeholder="请输入科目" v-model.trim="subject" />
      </div>
    </div>
    <div class="form-item">
      <div class="label">分数：</div>
      <div class="input">
        <input type="text" placeholder="请输入分数" v-model.number="score" />
      </div>
    </div>
    <div class="form-item">
      <div class="label"></div>
      <div class="input">
        <button @click="add" class="submit">添加</button>
      </div>
    </div>
  </div>
</div>
<script src="https://cdn.jsdelivr.net/npm/vue@2.7.16/dist/vue.js"></script>

<script>
  const app = new Vue({
    el: '#app',
    data: {
      list: [
        { id: 1, subject: '语文', score: 20 },
        { id: 7, subject: '数学', score: 99 },
        { id: 12, subject: '英语', score: 70 },
      ],
      subject: '',
      score: ''
    },
    computed: {
      Total() {
        //reduce适用于数组中数据的加减
        return this.list.reduce((sum, item) => sum + item.score, 0)
      },
      average() {
        if (this.list.length === 0) {
          return 0
        }
        //toFixed(2)保留两位小数
        return (this.Total / this.list.length).toFixed(2)
      }
    },
    methods: {
      del(id) {
        this.list = this.list.filter(item => item.id !== id)
      },
      add() {
        if (!this.subject) {
          alert('请输入科目')
          return
        }
        if (typeof this.score != 'number') {
          alert('请输入正确的成绩')
          return
        }
        this.list.unshift({
          id: +new Date,
          subject: this.subject,
          score: this.score
        })
      }
    },
  })
</script>